1. Field of the Invention
The present invention relates generally to stick formulations for the delivery of various therapeutic agents, such as anti-inflammatory agents, insect repellants, local anesthetics, antibiotics, and antifungal agents to skin and various mucosal surfaces of the body. Methods for using and making such stick formulations are also provided.
2. Background of the Invention
Agents applied topically to the skin are generally formulated in liquid or semi-solid formulations including creams, lotions, solutions, aerosols and ointments. Creams, lotions and ointments typically fall into one of four general classes: hydrocarbon bases, absorption bases, emulsion bases and water soluble bases and may be adapted to a variety of drugs. Although these types of formulations are widely used, they tend to be inconvenient and wasteful because of the difficulty in delivering a precise amount of such a preparation just to the area to be treated. This is particularly true of aerosols, which are subject to overspray and incidental inhalation of the product, as well as environmental concerns about propellants and disposal of containers. Ointments and creams are often messy and applied to a wider area than necessary because of their liquid or semi-liquid state. All of these products may also leave a wet, greasy or sticky feeling.
Stick products have been used for cosmetic purposes such as antiperspirants, deodorants, lipsticks and the like. Stick formulations have also been described that include analgesics dissolved in a particular ricinoleate vehicle, such as castor oil, prior to mixture in a stick (U.S. Pat. No. 4,048,309). These sticks must contain enough wax to remain solid, without trapping the active ingredient in the wax in a manner that would prevent drug contact with the skin. The method of manufacturing these sticks includes heating the formulation up to 90.degree. C. in order to melt the carnauba wax, which may cause separation of the components or degradation of the drugs.
U.S. Pat. No. 4,702,916, relates to formulations having 10-65% alcohol, 6-10% of an alkali metal salt of a saturated fatty acid gelling agent having from about C8 to about C22 lengths, about 10-30% water, and oleoresin capsicum, capsicum, capsaicin, camphor, allyl isothiocyanate, methyl nicotinate, menthol, and mixtures thereof. A semi-solid delivery system for hydrocortisone is described in U.S. Pat. No. 4,738,956 and incorporates a volatile silicone such as dimethicone or cyclomethycaine along with a fatty alcohol. These formulations are primarily designed for water insoluble agents and would be less efficient for delivery of water soluble products.
Considerations in preparing stick formulations for the delivery of an active ingredient, such as a drug, include the relative water solubility or lipid solubility of the active ingredient and the stability of the agent in the stick. These, and other technical considerations have continued to create problems in providing a stable and concentrated stick preparation. A need continues to exist for improved stick formulations that are convenient to use, non-messy, and formulated to deliver water soluble and/or water insoluble agents topically to the skin with good spreadability and stability.